This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. P22 head-tail connector (also known as portal proteins) is an oligomeric cone-shaped protein that connects the capsid to the tail of bacteriophage P22. The portal protein is also an integral component of the machinery that pumps DNA into the phage head. Each subunit of the oligomer has approximately 85.9KDa and the oligomer is expected to have a 12-fold rotational symmetry with overall size of ~1.1MDa. We have obtained crystals of the P22 head-tail connector under various conditions and tested cryogenic conditions on a rotating anode x-ray generator. The crystals have an average size of ~150*50*50 [unreadable]m3 and a perfect rectangular morphology. We hope to collect a high resolution data set and to determine the structure of the complex by using a cryo-EM low resolution electron density map as a starting model.